This invention relates to a metal working process, and particularly, to one adapted for the fabrication of a composite type disc brake rotor.
Many modern motor vehicles feature disc type brakes which employ a rotating rotor having a pair of separated parallel disc faces. Brake pads are actuated to compressively engage the rotor faces to create friction, thus providing a braking effect. While disc brakes in general are old, designers are continually striving to achieve improvements in their performance and efficiency. Moreover, there is a continuing desire to reduce the weight of all motor vehicle components. Such weight reduction goals are particularly important for components which constitute so-called "unsprung" weight that is defined as weight which is not mechanically isolated from road surface inputs by the vehicle suspension springs such as the tire, wheel, spindle, steering knuckle, axle, etc. Reductions in unsprung weight not only reduce total vehicle weight, but further improve vehicle ride and handling.
One approach toward reducing the weight of a disc brake rotor is to provide a so-called composite structure. Present designs for such rotors include a center "hat" section formed from stamped sheet metal which is loaded into a forging or casting machine. The cast or forged metal interlocks with the center section to form the separated disc faces of the rotor. The temperature of the metal surrounding the center section causes it to soften portions of the center section so that the two portions become mechanically fused. Further, mechanical features are provided for interlocking engagement between the components. Although composite disc brake structures according to the prior art have been found to be operable, several shortcomings of such designs have been observed. During the process of casting or forging the brake face portions onto the stamped metal center section, the intense heat of the process causes warping and irregularities to develop in the mounting surface of the stamped center section. Such irregularities may cause the brake surfaces to become misaligned from the rotor's axis of rotation when the rotor is mounted to the vehicle, thereby causing axial runout and out of roundness conditions. Accordingly, there is a present need to provide means for flattening and providing dimensional stability for the mounting surface of a composite brake rotor.
This invention provides means for achieving high dimensional control over the center section. Such control is provided through a process of "bubbling" a portion of the brake rotor center section such that the metal of the center section is strained in a radially inward direction to "stretch out" any irregularities. Thereafter, the deflected center "bubble" portion is removed through a blanking operation which provides a center clearance hole necessary for the associated vehicle's axle hub.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims, taken in conjunction with the accompanying drawings.